The present invention relates to a hinge assembly, and more particularly to a hinged manhole cover assembly that provides a safety lock for the cover.
Manhole covers are well known. Generally, a manhole cover is a removable plate forming the lid over the opening of a manhole to, among other things, prevent someone from falling in and to keep unauthorized persons out. Manhole covers often weigh more than 100 pounds, partly because the weight keeps them in place when traffic passes over them, and partly because they are often made out of cast iron, sometimes with infills of concrete. This makes them inexpensive and strong, but heavy. The often feature pick holes, in which a hook handle is inserted to lift them up.
Because of the weight of manhole covers, they often feature lift assemblies to assist users in opening and closing the covers. For instance, they may include a spring-assisted or gas-assisted cylinder connected between the cover and the frame to make them easier to open. As an added feature, some manhole covers, both manual and lift-assisted, include hinges on the frame and the cover to allow the cover to pivot between a closed position covering the manhole access opening, and an open position providing access to the manhole opening.
As an added safety feature to prevent a hinged manhole cover from swinging closed, it is known to provide a locking mechanism that holds the cover in the open position. One such cover includes a hinge assembly having a pair of rectangular tabs extending from the cover. Each tab fits into a slot on the frame. One of the tabs is seated on a ledge when the cover is in the closed position, and when the cover is moved to the open position, the tab falls off the ledge into a vertical slot that holds the cover in the open position until a user lifts the cover vertically to pull the tab out of the slot. Unfortunately, this arrangement suffers from a number of drawbacks. For instance, over time, dirt and other debris collects in the vertical slot, and, as a result, the tab no longer fits into the slot to lock the cover in the open position. This problem can be resolved by creating a hole, or “clean-out,” in the bottom of the slot that allows the dirt and other debris to fall through the slot and into the manhole opening, but the resulting cover assembly is no longer leak tight. In addition, the rectangular tabs pivot awkwardly when opening the cover, which can make manually lifted covers especially cumbersome to open.